Chronic lymphocytic leukemia (CLL) is susceptible to immune-mediated destruction as demonstrated by observations of the graft-versus-leukemia (GvL) effect after hematopoietic stem cell transplantation and donor lymphocyte infusion (DLI). Our preliminary studies demonstrate that DLI-treated CLL patients who developed GvL without apparent GvHD developed potent polyclonal B cell responses directed against antigens that are highly expressed in CLL and that mostly had perfect sequence identity between host and donor (and hence are not minor histocompatibility antigens). From these observations, we hypothesize that anti-CLL immunity can be further boosted by immunizing post-transplant patients with leukemia antigens combined with an adjuvant. Several unique characteristics of CLL support the rationale of developing this innovative therapeutic approach. Advanced CLL patients typically have high levels of circulating tumor, and thus tumor for vaccine generation is readily harvestable. As CLL patients are inherently immune-deficient, anti-tumor immunity is likely to be more effective after reconstitution of normal donor-derived immunity through allogeneic transplant. Finally, the potentially slow rate of disease progression in CLL patients should allow sufficient time for the development of immunity following transplant combined with several rounds of vaccination. Thus, we are actively recruiting patients to a newly opened phase I trial, in which we will administer irradiated autologous tumor cells as the source of leukemia antigens in combination with irradiated bystander cells expressing GM-CSF to patients with CLL following nonmyeloablative transplant. Studies at the DFCI have shown that local secretion of GM-CSF in the presence of irradiated tumor cells at the vaccination site can lead to destruction of tumor cells at distant sites of metastasis, reflecting development of anti-tumor B and T cell immunity. A recently engineered bystander cell line (called GM-K562 cells) will be used for this trial to secrete high and reproducible levels of GM-CSF at the site of vaccination, thus providing a consistent clinical reagent. In Aim 1, we describe the primary objective of the trial, which is to evaluate safety, toxicity and feasibility of the proposed treatment approach. As we anticipate the toxicity to be low based on previous GM- CSF trials, we will monitor the immunological effects of the vaccine by utilizing a set of assays that we have developed to measure antigen-specific B (Aim 2) and T cell (Aim 3) immunity against CLL-associated antigens. Novel aspects of this trial thus include: 1) vaccination of post-transplant patients with reconstituted immune systems;2) use of a novel engineered reagent for secretion of GM-CSF;3) detailed monitoring of anti-CLL immunity using a panel of CLL-associated antigens that we identified as targets of GvL;4) reduced intensity transplant as a platform for generating effective tumor immunity under acceptable conditions of toxicity. The studies will thus test an important hypothesis, provide a solid basis for further trials of tumor-based vaccines for CLL and further our long-term goal of generating curative, non-toxic immune-based treatment for CLL.